This invention relates to paper processing wherein individual sheets of paper or other media are separated from a stack of sheets and further processed. This type of operation is performed by electrophotographic equipment, as well as a myriad of other paper processing equipment. The processing includes the equipment manipulating or handling the paper in order to move the paper along a paper path. This invention can be used in conjunction with a wide variety of paper processing equipment, but was developed for use with electrophotographic equipment such as laser printers. The invention will be described in its application to electrophotography, it being understood that it also has applicability to other types of paper processing equipment.
Regardless of the particular configuration of the paper processing equipment, many have in common a paper pick, followed by a primary series of paper processing operations. The primary series of paper processing operations in the electrophotographic equipment, including the laser printer of the preferred embodiment is the imager station and fuser stations. This includes the laser printer of the preferred embodiment of this invention.
In electrophotographic printing, individual sheets of paper are taken from a stack of paper in a paper supply and a toner image, corresponding to a pattern of electrostatic charges, is applied to the paper. The removal of an individual sheet of paper from the supply is referred to as a "pick."
In the Assignee's Laser Jet printers, such as the Assignee's Laser Jet II-P.TM. printer, a pick is accomplished by a roller having an asymmetric profile, called a "D roller," rotating past a fixed pad. The D roller has a higher coefficient of friction with paper than the fixed pad and is spaced from the fixed pad so that only a single sheet of paper normally is moved by the rotation of the D roller. This generally accomplishes the desired pick of a single sheet of paper which is thereby fed to the electrophotographic imager, and subsequently ejected as a printed page.
An alternate technique for accomplishing a pick includes sliding a sheet from a stack of sheets in order to cause the top sheet to buckle. A corner separator is used to retrieve the buckled sheet, which is then fed to the electrophotographic imager and subsequently ejected as a printed page. This technique is used in the Assignee's Laser Jet 4L.TM. printer.
After the pick, an image is transferred to the paper at an imager, which may be a photoreceptor or other suitable equipment. The sheet is then further processed, usually passing a fuser station to a discharge tray. Additional paper processing may be performed, such as providing a dryer station (used in liquid imaging systems) and a discharge handler such as a paper collator. We use the term, "discharge" to refer to output or ejection of the paper, and such use is not a reference to electrostatic charge of the imager.
In the event of a sensed malfunction, a display on the printer indicates that the malfunction has occurred. The usual procedure requires the operator to investigate and remedy the malfunction, and press a "continue" or "operational reset" button. If the malfunction is a true paper jam, the equipment is partially opened, the wrinkled paper is removed from the paper path. Thereafter, the equipment is closed and the normal operation is continued upon pressing the button. On the other hand, the malfunction may be an empty paper supply. This of course does not require that paper be removed, but merely that the paper supply be replenished.
Paper jams can generate significant customer problems in laser printers. Most of the difficulties involve fuser jams, legal size paper timing malfunctions, Pick-up Delay jams (or no-pick jams), Pick Stationary jams, Delivery Stationary jams, and Initial Residure jams.
In a Pick-up Delay jam (or no-pick jam), the media does not reach a registration sensor within the required time after the start of pick-up. A Pick Stationary jam is the result of the trailing edge of a sheet of paper not reaching the registration position within the required time after the pass of the leading edge of the paper. This means that the time from sensing the leading edge to sensing the trailing edge at the registration position is excessive.
A Delivery Stationary jam is the result of a delivery or forward sensor, located at an output of the imager, failing to detect a sheet of paper in the required time after the output of a Vertical Sync signal. The Vertical Sync signal is merely a reference to the start timing of a print cycle, so the Delivery Stationary jam is an indication that a picked sheet does not make it to the forward sensor after being sensed at the output of the pick mechanism.
The terminology, "Initial Residure," refers to media being resident in the equipment at locations other than the paper supply. In an Initial Residure jam, the delivery sensor or registration sensor detects or senses the media at a required time after power-on. This is an indication that the sensor is blocked, for example, by a sheet of paper in the paper path.
The response to a paper path malfunction has typically been to discontinue operation of the printer until the jam could be cleared by the operator. In reality, there are different ideal responses to different types of paper jams. If the jam is one of slow feed, then if the paper is eventually picked up by the pick mechanism, then the malfunction has self corrected and the printer should continue operating. If the malfunction is the result of an accordion jam at the fuser station (near the output of the printer), the continued operation of the printer's paper processing mechanism will probably make the jam worse. Likewise, if the malfunction is the result of a paper wrap at the fuser station, the continued operation of the printer's paper processing mechanism is also not advantageous.
It has been noted that malfunctions in the paper path which are sensed at the output of the pick mechanism are not likely to become significantly more difficult to clear, even if the paper processing mechanism is permitted to remain in operation and the jam is not corrected. As an example, an accordion jam at the output of the pick mechanism would probably not be self-clearing, but continued operation of the paper processing mechanism would not make the jam worse, unless a subsequent sheet is picked. It is likely that permitting the paper processing mechanism to continue operating would merely further bunch the paper and make it easier to extract from the printer. In any case, paper jams at the input of the printer tend to be easiest to manually clear because of their accessibility.
Some printers simultaneously process multiple sheets of paper by effecting a pick operation prior to the ejection of a preceding sheet. Therefore, while a pick operation is being attempted, the preceding sheet may be passing through the fuser station and being processed at the paper discharge portion or output of the printer. If the pick operation is unsuccessful, then having the printer stop when the malfunction is detected will cause a malfunction in printing the preceding sheet. This causes a failed print result on the first sheet, perhaps with unfused toner remaining on the first sheet.
It would be advantageous if the printer were programmed to determine what the most appropriate sequence of operations should be in response to particular paper path malfunctions. In particular, it would be advantageous if the printer could make a determination as to whether the appropriate response to a sensed malfunction is to immediately stop, ignore the malfunction, or continue operation for enough time to clear any remaining sheets and attempt to clear the jam. For similar reasons, it would be advantageous if, in response to a sensed malfunction, a printer did not stop in circumstances which are likely to leave paper in the fuser.
A common error occurs when paper length is used to determine correct function. A common change of paper size is between a letter size sheet and a long size sheet. Typical changes between sizes are between letter size such as A-4 (21.0.times.29.7 cm) or 81/2.times.11 letter (21.59.times.27.94 cm) and size such as B4 (25.7.times.36.4 cm), U.S. 81/2.times.14 legal (21.59.times.35.56 cm) or oficio (21.59.times.33.02, used primarily in Italy). These size changes could be either inadvertent as a result of the wrong size sheet inserted into the printer's paper supply, but it is possible that the user intends to use the size paper which is in the tray but has not inserted the software commands for the paper size into the print command of the user's program. As a practical matter, the most common paper size error which affects paper processing is between 81/2.times.11 letter and U.S. 81/214 legal, or between A-4 and U.S. 81/2.times.14 legal. Paper size errors between A-4 and 81/2.times.11 letter are also common, but involve only a 2 cm length discrepancy.
If the printer expects a shorter paper size than is actually loaded into the paper supply, then the trailing edge of the sheets will clear the various portions of the printer later than expected. It is therefore possible that a subsequent pick in a multiple series of sequential pick operations could result in the pages overlapping. This means that in order to ignore paper size errors, the paper processing mechanism must delay printing sequential sheets until enough time has passed for the longest expected sheet to pass. This slows operation of the printer significantly more than if the timing of sequential picks is made to accommodate a narrow range of paper sizes.
The detection of different paper positions usually can be accomplished by sensors at several positions along the paper path. Thus, if the paper size is wrong, a paper size malfunction is detected.
The result of a paper size error is that the printer reports a malfunction. In some cases this is desirable because the wrong size paper is in fact being used, but in other cases it is desirable that the error be ignored. Again, it is advantageous to permit the sheet to proceed to discharge (eject) so as not to stop at the fuser station or otherwise require clearing of the printer. If the paper size error is used to stop the equipment and the user wishes to continue with the "wrong" size paper, the user may have to repeatedly restart the printer for subsequent sheets of paper in a print job.
In other cases, the receipt of a "wrong" size paper error is merely one of improper programming or the result of no page size command being provided either directly to the printer or to the printer through software commands. There are still other cases in which the operator will deliberately wish to use the "wrong" size paper. An example of this is the case in which a document is prepared for printing on A-4 paper, but is to be initially printed on 81/2.times.11 letter (21.59.times.27.94 cm) paper, using the A-4 formatting. Since page size is also used to determine the timing of successive picks, it is important that the printer accommodate changes in paper size even though the user may otherwise wish to permit printing on the "wrong" size paper.
In a few cases, a size error results from a default paper size being different from the actual common type of paper. As an example, if the common paper is A-4 and the default paper size is 81/2.times.11 letter, then the paper size error would occur each time the software print command does not have the paper size command. While geographical distribution, and in some cases even line current, may be used to set the correct default size, this is not always reliable. Thus, a user with the different type of standard paper must frequently address a paper size error malfunction.
The change between letter size and legal size paper is the most common. Printed program material often need not be reformatted for the paper size change. If a program does not issue a paper size command (or the command is not inserted into the program's output document or file), the paper size command must be manually programmed to the printer. In some situations, particularly single user applications, the paper size is visibly apparent, and so it would be desirable if the printer automatically adjust for paper size error. Automatic adjustment would eliminate the need for the user to program a paper size command.
It would therefore be advantageous if the printer could be made to selectively accommodate the different page size, or could in some circumstances ignore or accommodate the unexpected page size.